I am getting chicks from a family hatchery, and I have been daydreaming about those chicks giving me more chicks! It struck me suddenly though, that I may not be able to allow them to breed!
I am aware that an offspring can be bred back to its parent but siblings should not breed. Is it most likely that the chicks I have ordered all came from the same parents, are siblings, and therefore cannot be bred if I happen to get a rooster in my chick order?

It isn't ideal, but you've no choice. Start with what you have and then breed them, going forward, according to the plan. A 2 "group" plan, etc. There are a few ways of doing this in subsequent generations, breeding daughters back to father, sons back to mother, etc. Lots of folks begin with a related trio and then go from there. You gotta start with what you have.

I'd say its possible, but not likely they all have the same parents. There's lots of mothers per breed, and a few daddies. Its more likely they share a dad than a mom, so there is a little variety that way.

Let's say there's 20 hens and 2 roos. Ignoring the off days, there are 20 eggs a day from, and let's say the hatchery does an order of a weeks worth of eggs, so that's 140 chicks (perfect hatch). If you want 10 of them, the likelyhood that all 10 have the same dad is low, but definitely a reasonable possibility. It is impossible for them all to have the same mom, because there are only 7 eggs from each mom. Its more likely that each chick has a different mom than it is to have any duplicates just because there are so many moms to choose from.

With all those possibilities, that you'd get two chicks that have the same mom and dad, is darn near impossible. It is likely you could choose 2 chicks that have the same dad, but i wouldn't worry about it. Inbreeding isn't as big a deal in animals as it is humans. Alot of show dogs are inbred at some point in their lineage to get desirable traits.

Thank you! I was sitting here wondering if I would have to get a whole new lot of chicks from a totally different hatchery JUST to get a rooster!
This now branches off into a new question. How many generations should I allow to breed with dad/mom/grandma/grandpa before introducing new blood or a new rooster to my flock?

If your flock is good enough, you will never need to introduce new blood. I know many old time show breeders that started with a trio and haven't introduced any new blood in 50 years. Their flocks get so uniform and predictable that when you bring in new blood, you mess everything up and it can sometimes take years to get it back to where it was.

I used to breed Rex rabbits for show. I used the same buck for 6 generations of his daughters and never had any type of deformities or anything like that. The biggest key is to select and keep for breeding only the very very best animals. If you are trying to breed to the Standard of Perfection then you only keep those that are the closest to that standard. If you are just breeding for fun then just breed for the things you like. At that time I sold rabbit meat, so I would raise 100 babies and only keep the very best 3 does and possibly 1 buck out of 100.